On Wed, 30 Jun 2010, Philippe Cerfon wrote:
> g) There are some howtos which say one should create PVs on partitions
> rather than whole devices, while other say it's fully ok to have them
> directly on the device.
> But I think this must also have an impact on all the alignment as I
> have 63 more 512 sectors, right? So how should I best do this?
>
> I read $ cat /sys/block/sda/sda1/alignment_offset
> 0
> which I don't understand. I thought having the 63 sectors partition
> table in the beginning should destroy the alignment?
I can answer this one. Using no partition table makes alignment
slightly easier, but is dangerous if the disk is ever seen by another
OS - which may think it is unformatted and do something nasty. On
the other hand, the partition types LVM and RAID simplify reliable
booting (especially for software RAID).
When using a parition table, it must be created with a size that doesn't
destroy alignment - e.g. 128 or 256 sectors. This is a lot of wasted space
for the useful byte (the partition type), but is trivial compared to
disk sizes these days, and lets other Wintel OSes know there is data
on the disk.
My rule of thumb is that I skip the partition table for permanent local
LVM drives unless the drive also contains software RAID or a /boot partition.
--
Stuart D. Gathman <stuart bmsi com>
Business Management Systems Inc. Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
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